Organopolysiloxane compositions which are cured by the addition of Si-bonded hydrogen to Si-bonded aliphatic multiple bonds are well known in the art. For example, U.S. Pat. No. 3,419,593 to Willing discloses that an .tbd.SiH group can be reacted with any silicon compound which contains aliphatic multiple bonds in the presence of a platinum compound such as chloroplatinic acid. While the cure rate of these organopolysiloxane compositions is substantially accelerated with the platinum catalysts, the "pot-life" or working time is substantially decreased. Therefore, it would be desirable to have an organopolysiloxane composition which utilizes a platinum catalyst and cures to an elastomer at an elevated temperature, but has a longer "pot-life" or working time.
Several methods have been proposed to improve the stability of platinum catalyzed organopolysiloxane compositions by adding certain reagents to retard crosslinking at room temperature. Several of the retarding agents used for this purpose are tin compounds such as described in U.S. Pat. No. 3,532,649; isocyanurate compounds such as described in U.S. Pat. No. 3,882,083; sulfoxide compounds such as described in U.S. Pat. No. 3,453,234 and aminosilanes, such as described in U.S. Pat. No. 3,723,567. Other retarding agents which have been used are acetylenic compounds such as those described in U.S. Pat. No. 3,445,420 or compounds having at least one monovalent group of the formula ##STR1## such as described in U.S. Pat. No. 4,077,937.
Many of the retarding agents described above have the disadvantage that they must be used in large amounts, which eventually result in a decrease in the cure rate and thus provide for insufficient cures even at elevated temperatures. The use of acetylenic compounds has the disadvantage that the use of a compound having a relatively low boiling point tends to decrease the stability of the composition even at room temperature due to loss on evaporation. Likewise, a compound having a relatively high boiling point often results in an unsatisfactory cure even when subjected to heat.
It is, therefore, an object of the present invention to provide organopolysiloxane compositions which are substantially free from crosslinking at room temperature under anhydrous conditions. Another object of the present invention is to provide organopolysiloxane compositions which utilize .tbd.SiH containing compounds. Still another object of the present invention is to provide organopolysiloxane compositions which are heat activated. Still another object of the present invention is to provide platinum catalyzed organopolysiloxane compositions which are substantially free of crosslinking at room temperature under anhydrous conditions in the absence of additional retarding agents. A further object of the present invention is to provide organopolysiloxane compositions which utilize a mixed crosslinking system. A still further object of the present invention is to provide organopolysiloxane compositions having improved adhesion to substrates which generally poison platinum catalyzed systems.